The basic syntax allows us to specify one host group. Although we mentioned earlier that aggregating across arbitrary hosts would require creating a new group, there's one more possibility—an aggregate item may reference several host groups. If we modified our aggregate item key to also include hosts in a Solaris servers group, it would look like this:
grpavg[[Linux servers,Solaris servers],system.cpu.load,last]
That is, multiple groups can be specified as comma-delimited entries in square brackets. If any host appears in several of those groups, the item from that host would be included only once in the calculation. There's no strict limit on the host group count here, although both readability and overall item key length limit—2,048 characters—should be taken into account.
Both calculated and aggregate items can reuse values from any other item, including calculated and aggregate items. They can also be used in triggers, graphs, network map labels, and anywhere else where other items can be used.